Sentinel lymph node biopsy status correlates with postoperative stimulated thyroglobulin levels in low-risk papillary thyroid cancer patients

Objective: Radioactive iodine (RAI) remnant ablation in low-risk papillary thyroid cancer (PTC) is controversial. Current patient selection guidelines recommend the use of postoperative stimulated thyroglobulin (stim-Tg), neck dissections, and sonography but fail to include sentinel lymph node biopsy (SLNB). The objective of this study was to evaluate the correlation between SLNB status and postoperative stimulated thyroglobulin as a surrogate marker of clinical outcome.Methods: Retrospective chart review of low-risk PTC patients who underwent a total thyroidectomy with SLNB at the McGill Thyroid Cancer Center. SLNBs were obtained using methylene blue dye. Biochemical measurements were acquired between 4 and 12 weeks postoperatively. Statistical analyses were performed using logistic regression models and receiver operating characterisitc (ROC) curves. A P-value <.05 was considered significant.Results: Ninety-six patients were included in this study. The positive SLNB rate was 14.6%. The mean postoperative Tg level was 1.41 μg/L. There were no significant correlations between the SLNB and the covariates analyzed (age, gender, histology, tumor size, and thyrotropin levels). Patients with negative SLNB were significantly more likely to have a lower stim-Tg (P<.0001). When postoperative Tg was analyzed as a categorical variable, a threshold of <1 μg/L was significantly associated with a negative SLNB, with a sensitivity and specificity (determined by ROC curves) of 0.86 and 0.88, respectively. Conclusion: There exists a correlation between SLNB and postoperative Tg. This creates the possibility of a new approach to RAI administration among low-risk PTC patients incorporating SLNB to the current guidelines.